The invention relates to a method in continuously operated unwinding of a paper reel, in which a paper reel wound on a reeling core or the like is unwound by rotating the same to guide the paper web to a further processing stage.
In particular, the target of application of the method is a method used in connection with the unwinding of so-called machine reels which are full and reeled up on the reeling core from a full-width web. Naturally, the invention is not restricted solely to the above-mentioned embodiment, but it can be applied in unwinding in general as well as for collecting information process during the reeling up process for enhancing the control of the unwinding.
It is economically reasonable to try to unwind all the paper web that has been reeled up and to guide it to a further processing stage, such as supercalendering, coating machine or printing machine, etc. On the other hand, a successful further processing of the paper web requires the paper reel that has been reeled up to be of good quality, in other words the paper web passed from the paper reel that is being unwound is of such good quality that further processing can be successful and disturbances or breaks do not occur.
On the other hand, especially when conventional reeling up techniques are utilized in the reeling of thin paper grades (weight max. 60 g/m2) in particular, it is possible that due to the conditions of the reeling process, for example the low tension of the paper web, there are local changes deviating from the circular form of the cross section of the paper reel, typically protrusions in the direction of the radius, which result from local wrinkling of the paper web or from tearing of the paper web. Such mechanical defects occurring in the paper web that is being reeled up cause the breaking of the paper web, at the worst, or at least problems at the further processing stage, if they are not taken into account. The occurrence of the aforementioned defects which are effective in the unwinding of the paper web may be caused by various factors, or by cooperation of the same. Such factors include e.g. the paper grade, grammage of the paper, friction factor of the paper web, diameter of the paper reel, tightness of the paper reel, condition of the reeling core, as well as the dimensions of the reeling core. Because the number of effective factors is as large as it is,there may be occasional variations in the quality properties of the paper reel, especially in the bottom area of the paper reel. This contingency has caused problems especially when the aim is to attain continuous unwinding i.e. good runnability, in other words to avoid breaks. Because of occasional defects in the quality of the paper reel, part of the bottom area of the paper reel is left unwound, to avoid problems caused by occasionally occurring defects in the paper reel. Typically 2 to 5% of the unwound paper reel is thus not utilized at the further processing stage.
It is an aim of the present invention to solve the above-described range of problems in such a manner that during the unwinding process, the entire defectless part of the paper reel can be guided to further: processing, at the same time ensuring that said paper reel does not contain defects originating from the reeling up process impairing the quality of the paper web that is being unwound. If such defects occur, they can be detected and analysed at such an early stage that .e.g. the continuous unwinding can be maintained by slowing down the further processing and unwinding stages (the defect is passed by cautiously), by guiding the defect point past the further processing stage or by changing the paper reel to be unwound.
To attain these objectives, the method according to the invention is primarily characterized in that the shape of the outer surface of the paper reel is measured, advantageously in the cross-sectional plane of the paper reel. The cross-sectional plane of the paper reel refers to the plane preferably perpendicular to the longitudinal direction of the central axis of the paper reel. By measuring the shape of the outer surface of the paper reel, it is possible to attain information on the local changes in the radius/diameter of the paper reel that is being unwound, which changes are then compared to a reference level prevailing at the moment, such as the average value of the radius/diameter.
Surprisingly, it has been observed in this invention that a defect generated during the reeling up of the paper reel, especially a defect occurring in the edge areas of the paper reel, affecting the quality of the paper web, can be detected from the paper reel that is being unwound well before the point of the web in question becomes unwinded. Such a defect shows up in the shape of the cross-section of the paper reel several laps before it enters the unwinding stage, as a point of discontinuity which is local, periodical or occurs in a given angular sector and can be detected. The observation related to the occurrence of the defect point can be analysed immediately by means of a computer, and on the basis of this analysis it is possible to give the necessary instructions to the unwinding and further processing stages, for example according to a predetermined strategy of action.
The other dependent claims present some advantageous embodiments of the method according to the invention.
The invention also relates to an apparatus in continuous unwinding of a paper reel, in which a full paper reel wound on a reeling core or the like is arranged to be unwound by rotating the same to guide the paper web to a further processing stage. The apparatus according to the invention is primarily characterized in that the apparatus comprises means for measuring the shape of the cross-section of the paper reel.
The other dependent claims present some advantageous embodiments of the apparatus according to the invention.